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Optimisation of the Reaction Parameters in a Batch Reactor and a CSTR for the Recovery of Phenol from Hydrothermal Biomass Liquefaction

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Optimisation of the Reaction Parameters in a Batch Reactor and a CSTR for the Recovery of Phenol from Hydrothermal Biomass Liquefaction Optimisation of the reaction parameters in a batch reactor and a CSTR for the recovery of phenol from hydrothermal biomass liquefaction zur Erlangung des akademischen Grades eines DOKTORS DER INGENIEURWISSENSCHAFTEN (Dr.-Ing.) der Fakultät für Chemieingenieurwesen und Verfahrenstechnik des Karlsruher Institut für Technologie (KIT) genehmigte DISSERTATION von Dipl.-Ing. Daniel Forchheim1,2 aus Karlsruhe Referent: Prof.Dr. Michael Türk1 Korreferentin: Prof.Dr. Andrea Kruse2 Tag der mündlichen Prüfung: 25.03.2014 1 Institut für Technische Thermodynamik und Kältetechnik 2 Institut für Katalyseforschung und -technologie Acknowledgements An dieser Stelle möchte ich besonders meinen Eltern danken, die mich mein Leben lang unterstützt haben, der Forschung und den Wissenschaften nachzugehen. Ich danke Andrea Kruse und Uschi Hornung, die mir mit vielen Hinweisen und in zahlreichen Gesprächen wichtige fachliche Unter- stützung und Vertrauen in meine Arbeit entgegengebracht haben. Ein beson- derer Dank gilt James Gasson, dessen Kooperation wesentlich die kreativen Momente dieser Arbeit gefördert hat. Ferner hätte ich die praktischen Ex- perimente nicht ohne die tatkräftige Unterstützung vieler Menschen am IKFT durchführen können. Stellvertretend möchte ich hier Birgit Rolli, Thomas Tietz, Matthias Pagel, Sonja Habicht und Armin Lautenbach nen- nen. Auch ohne die Zuarbeit vieler Studenten wäre diese Arbeit in den let- zten Jahren nicht bis zu diesem Punkt gereift. Herzlich danken möchte ich deshalb David Steinbach, Tatjana Sutter, Jonathan Jeras, Philipp Kempe, Saskia Lamour, Lucile Courtinat, Yichie Chien, Yali Liu, Matthew Schu- macher, Stephanie Hauschild und Alvaro Herreras. Sie alle haben maßge- blich zum Gelingen dieser Arbeit beigetragen. Schließlich möchte ich meiner kleinen Familie danken, die mich täglich getragen hat und immer die men- tale Stütze war, auch wenn an manchen Punkten Unmut, Demotivation oder Verzweiflung geherrscht haben. Meine Frau Raquel und mein ungeborenes Kind haben mir immer die Kraft gegeben, die ich brauchte, um diese Arbeit bis zum Ende zu führen. Abstract The recovery of platform chemicals from biomass gains a growing govern- mental, economic and public interest. This work deals with the hydrothermal liquefaction of lignin. The focus laid on the discovery of the main reaction pathways within the depolymerisation of the lignin-macromolecules, the dis- covery of bottleneck reactions and the investigation of reaction mechanisms. In this context also the influence of the solvent as well as the influence of catalysis were studied. This was achieved by intensive literature study and experimental work in both batch and continuous reactor. Simulation of the thermodynamic equilibrium as well as modelling of the formal kinetics of the discovered reactions facilitated the evaluation of experimental results. The aim of this work was to provide tools for the optimization of process parame- ters and to indicate the direction for further studies regarding the conversion of lignin into phenolics. Thus, the economic feasibility of different process scenarios was studied in order to evaluate the attractiveness of a technical process. Solvent studies involved the comparison of hydrothermal lignin depoly- merisation and lignin solvolysis in ethanol. Lignin depolymerisation was found to be faster in water than in ethanol at moderate temperatures (633 K). Furthermore, the comparison of both solvents, water and ethanol, showed that water leads to a narrower spectrum of phenolic products and a tenfold increase of the catechol yield. This is advantageous in respect to the separa- tion of the phenolic product from solvent and by-products. The simulation of the thermodynamic equilibrium with Aspen Plus V7.2 showed that the ma- jor part of any organic input material including 100 % of the solvent ethanol at 633 K would be converted into gaseous components while water showed to be resistant against thermal decomposition. Heterogeneous catalysts showed very positive effects on the hydrodeoxygenation of primary or secondary phe- nolic products from hydrothermal lignin depolymerisation. The application of Raney-Ni e.g. selectively catalyses the conversion of catechol into phe- nol. Among the phenolic products recovered from the lignin degradation phenol is currently most utilized in the chemical industry. Kinetic modelling aided in the validation of the a priori model of reaction pathways and the discovery of bottleneck reactions within the lignin depolymerisation. It was proven that certain reactions can be predicted by the origin of the lignin, or the utilized solvent. Especially the influence of the chosen reactor was elucidated. Employing a Continuous Stirred Tank Reactor (CSTR) facili- tates capping reactions, which leads to reduced yields of solid residue and gaseous products. At the same time it favours the formation of phenolic i products. Elucidating reaction mechanisms contribute to the explanation of these phenomena. The production of phenol from lignin by solvolysis in ethanol or hydrothermal degradation is economically not feasible if the cur- rent state of the art is considered. Studies of different scenarios showed that yields of phenol and other phenolics from lignin should be increased from at most 10 % to at least 20 % while the lignin/solvent ratio must increase and the mean residence time must be reduced in order to reduce especially the capital related costs. Zusammenfassung Die Gewinnung von Plattformchemikalien aus Biomasse bekommt wach- sende Aufmerksamkeit seitens Regierungen, Wirtschaft und Öffentlichkeit. Diese Arbeit beschäftigt sich mit der hydrothermalen Verflüssigung von Lignin. Der Fokus liegt auf der Entdeckung der Hauptreaktionspfade, welche die Depolymerisation der Ligninmoleküle umfasst, vor allem der kritischen Reaktionen sowie der Erforschung der Reaktionsmechanismen. In diesem Zusammenhang werden auch der Einfluss des Lösungsmittels und der Kata- lyse diskutiert. Dies sollte erreicht werden durch intensive Literaturstudien und Laborexperimente im Batchreaktor und im kontinuierlichen Rührkessel. Die Simulation des thermodynamischen Gleichgewichts sowie das Model- lieren der Formalkinetik der postulierten Reaktionspfade zeigten sich als probate Mittel für die Evaluierung der Versuchsergebnisse. Das Ziel der Arbeit war es, Werkzeuge für die Optimierung der Prozessparameter verfüg- bar zu machen und die Richtung für weiterführende Studien der Ligninver- flüssigung aufzuzeigen. Dazu gehörte auch eine Machbarkeitsstudie, welche das wirtschaftliche Potential eines technischen Prozesses zur Gewinnung von Phenolen aus Lignin evaluiert. Zur Untersuchung des Lösungsmitteleinflusses wurde ein Vergleich zwi- schen hydrothermaler und solvolytischer Spaltung in Ethanol herangezogen. Die Lignin-Depolymerisation war bei moderaten Temperaturen (633 K) in Wasser schneller als in Ethanol. Ferner zeigte der Vergleich zwischen Wasser und Ethanol, ein engeres Produktspektrum bei hydrothermaler Spaltung von Lignin. Gleichzeitig stiegen die Catechol-Ausbeuten um das Zehnfache. Dies bietet vor allem Vorteile in Bezug auf eine Produkttrennung von Lö- sungsmittel und Nebenprodukten. Eine Simulation mit Aspen Plus V7.2 zeigte, dass der größte Teil der organischen Komponenten inklusive 100 % des Lösungsmittels Ethanol im thermodynamischen Gleichgewicht bei 633 K in Gas umgewandelt würden. Wasser hingegen ist sehr resistent gegen ii thermische Zersetzung. Heterogene Katalysatoren zeigten positive Effekte bezüglich der Hydrodeoxygenierung von primären oder sekundären pheno- lischen Produkten der hydrothermalen Lignin-Depolymerisation. Der Ein- satz von Raney-Ni katalysierte beispielsweise selektiv die Umwandlung von Catechol in Phenol. Unter den phenolischen Produkten, die bei der Lignin- zersetzung entstehen, ist Phenol derzeit die gängigste Plattformchemikalie in der chemischen Industrie. Kinetische Studien halfen, die a priori postulierten Modellreaktionen zu validieren und die kritischen "Flaschenhals"-Reaktionen ausfindig zu machen. Es konnte gezeigt werden, dass verschiedene Reak- tionen vorhergesagt werden können, wenn beispielsweise die Herkunft des Lignins oder das eingesetzte Lösungsmittel berücksichtigt werden. Beson- deren Einfluss hat auch der Einsatz verschiedener Reaktortypen. Ein kon- tinuierlicher Rührkessel erleichtert die Sättigung von Radikalen, was zu einer reduzierten Ausbeute von festen Rückständen sowie gasförmigen Produk- ten führt. Gleichzeitig wird die Entstehung von phenolischen Produkten gefördert. Wesentliche Erkenntnisse über die Reaktionsmechanismen trugen zur Erklärung dieser Phänomene bei. Die Phenolgewinnung aus Lignin durch hydrothermale oder solvolytische Spaltung in Ethanol ist unter Berücksich- tigung des aktuellen Stands der Technik wirtschaftlich nicht machbar. Die Studie verschiedener Szenarien zeigte, dass die Ausbeuten von phenolischen Produkten von etwa 10 % auf mehr als 20 % steigen sollten, wobei gleichzeitig das Lignin/Lösungsmittel-Verhältnis deutlich steigen und die Verweilzeit im Reaktor deutlich gesenkt werden muss um vor allem die Kapitalkosten für die Anlage zu senken. iii iv Contents Abstracti Glossaries ix Glossary................................. ix Acronyms................................ ix Symbols................................. xi 1 Introduction1 1.1 Motivation............................1 1.2 Background and state of the art.................4 1.2.1 Lignin...........................4 1.2.2 Chemical reaction mechanisms.............7 1.2.3 Solvent..........................8 1.2.4
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